Study On The Migration,Leaching And Bioavailability Of Different Magnesium Fertilizers In Soil

Magnesium?Mg?is a mineral nutrient necessary for plant growth and development.Mg is the central atom of chlorophyll,and is also an activator of various enzymes which participate in various metabolic reactions in plants,Magnesium deficiency can affect the normal growth and yield quality of crops.In last decades,with the large-scale application of fertilizers and the lack of magnesium fertilizers,and the removal of magnesium by crop and soil leaching,the deficiency of magnesium in the southern soil-crop system is becoming more and more common.Application of magnesium fertilizer has become an important measure to improve crop yield and quality,Then understanding the movement and leaching characteristic of different Mg fertilizers in Mg deficient soil is of importance for rational application of Mg fertilizers.Indoor soil column simulated experiment was conducted to study the effectiveness,movement and leaching characteristics of Mg from four Mg fertilizers including magnesium oxide?MgO?,improved magnesium sulfate?improved MgSO₄,pH>8.0?,calcium magnesium phosphate fertilizer?CaMgP?and potassium sulphate magnesium?KMgS?on three typical acid Mg-deficient soil?red soil,yellow soil and purple soil?from South China.Then,on this basis,pot experiments with maize were conducted to study the bioavailability of different Mg fertilizers on acidic Mg-deficient soils,and the effects of different Mg fertilizers on corn physiological parameters and nutrient uptake were further clarified.Both will provide a support for the rational use of Mg fertilizers on acid soils.The results of indoor soil column simulated experiment showed that:Different magnesium fertilizer types,soil types and magnesium fertilizer use significantly affected the movement and loss of magnesium in the soil.1)After 60-day leaching period with simulated rainfall of 1000 mm,a strong downwards movement of soil Mg by application of MgO,improved MgSO₄ or KMgS fertilizer in these three soils was observed.Compared with no Mg treatment?CK?,the soil exchangeable Mg concentrations in soil layers without Mg application?15⁵0 cm?were significantly increased by a range of 17.9¹05.4 mg kg^-1 due to Mg application in top layer?0¹5cm?.2)In generally,Mg concentration in leachate showed an increased and then decreased trend,which could be simulated well by quadratic equations.Accordingly,the amount of leached Mg under different Mg treatments could be matched well by exponential equations.The accumulated content of leached Mg on the yellow soil ranged 25.4 to 84.8 mg kg^-1,which was close to that on the purple soil,and which was 2³ times higher than that on red soil.3)After the leaching experiment,the leaching ratio of the applied MgO,improved MgSO₄ and KMgS fertilizers on yellow soil was as high as 33.1%,42.2%and 55.6%(Magnesium oxide equivalent to 225 kg ha^-1),respectively.Increased Mg concentration(Magnesium oxide equivalent to 450 kg ha^-1)will significantly increase the loss rate of Mg?76.5%,60.3%and 102.7%?;and these ratios were similar with that on purple soil but much higher than that on red soil.On the other side,application of CaMgP fertilizer could increase the retention of Mg in soil,slow down the downwards movement of Mg,resulting less leached Mg during the leaching experiment period than CK treatment.4)The soil exchangeable Mg in 0¹5 cm soil layer of the three soils was increased from 20.0⁹6.3 mg kg^-1 to 64.2⁸60.0 mg kg^-1by application of different Mg fertilizers.Among the four Mg fertilizers,improved MgSO₄?pH>8.0?showed the highest effectivity on improving soil exchangeable Mg,followed by CaMgP,MgO and KMgS,respectively.5)By integrated consideration of effectiveness for Mg availability,Mg retention by soils,Mg leaching characteristics in soil and the remediation of soil acidification,CaMgP fertilizer is recommended for all the three typical acid soil in South China;while the improved MgSO₄ fertilizer is more suitable for the clay-enriched red soil.Magnesium oxide,could be used on red soil for soil Mg retention due to its slow-released property.The KMgS fertilizer is suggested as topdressing fertilizer because of its easy leaching characteristics and high availability of both Mg and potassium?K?.The results of pot experiment with maize showed that:1)The application of Mg fertilizers significantly promoted the growth and development of corn.The application of magnesium fertilizer significantly increased maize plant height?3.7²1.0%?and relative chlorophyll content?3.0³7.0%?,corn stalk?53.1¹08.6%?and shoot biomass?57.6¹65.5%?.2)The application of Mg fertilizer significantly promoted the accumulation of Mg in maize by 2.3¹1.8 folds.Among the four types of Mg fertilizers,improved MgSO4 and CaMgP fertilizers showed the best effect.3)Due to the antagonism of K and Mg,the high K level reduced the translocation of Mg from soil to shoot and thus decreased the Mg accumulation in the shoot parts.4)The application of alkaline Mg fertilizers reduced the acidity of soil.Especially,improved MgSO₄ and CaMgP fertilizers significantly increased the pH value of soil by 1.0¹.5 units.In summary,the application of Mg fertilizer can increase the chlorophyll content of corn and magnesium accumulation in each part of corn,and thus increase the biomass of maize plants.However,the application of high dosage of K fertilizer resulted in the reduced growth and development of maize,decreased Mg accumulation of the shoot part of corn,but increased Mg accumulation in the root of maize.Combined the pot experiments with the indoor soil column experiment,CaMgP fertilizer applied to the yellow soil and purple soil had a lower leaching loss but higher bioavailability for plants.